Exhaust silencer



Feb. 9, 1937. H. H. coucH ET AL. 2,069,751

EXHAUST S ILENCER H. H. COUCH ET AL Feb. 9, 1937.

EXHAUST S ILENCER 2 Sheets-Sheet 2 INI/ENTOR HOWARD H. OUCH DUD'LEY W. WHT/(INS BY JAMES B. BHELSFORD Filed May 15, 1933 'I'TORNETJ Patented Feb. 9, 1937 UNITED STATES EXHAUST SILENCER Howard H. Couch, Oakwood, Dudley W. Watkins,

Patterson Field, and James B. Brelsford, Dayton, Ohio,

Application May 15, 1933, Serial No. 671,184

12 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon.

This invention relates to devices for silencing pressure pulsations of gaseous mediums passing therethrough. More particularly, this invention relates to exhaust silencers for explosive engines and is especially designed for use in connection l() with aircraft engines.

The exhaust gases coming from an internal combustion engine flow in pulsation and the noises incident thereto are essentially due to the explosion in the engine cylinders, the vibrations of the conductor of these gases from the engine, and the impacts of the gases against the atmosphere as it leaves the conductor.

This invention has for one of its objects the provision of a silencer in which a passageway or channel is surrounded by a series of side branches disposed successively along the length thereof. These side branches are connected with the passageway and are so constructed and arranged as to reduce the noises to a minimum and to alternate the pulsations of the exhaust of the internal combustion engine to which the silencer is connected.

It is a further object of this invention to provide a silencer that is small in size and low in 30 weight for a given horsepower, the crosssectional area of which is slightly greater than that of the exhaust pipe, resulting in a silencer which has but very little more drag than the regular exhaust pipe.

35 Certain other objects and advantages will appear and be appreciated from the detailed description of the invention taken in connection with the accompanying drawings which show several embodiments of this invention.

40 Referring to the drawings:

Fig. l is a bottom plan view of a silencer embodying our invention with parts broken away;

Fig. 2 is a sectional view taken on line 2-2 of Fig. 1;

V45 Fig. 3 is a longitudinal sectional View taken on gases and one or more series of chambers distributed lengthwise of said channel and surrounding the same to provide a series of sections that have communication with the channel and with the atmosphere. The innermost chambers of each section are in direct communication with the channel and the outer or superimposed chambers have communication with the channel indirectly through correspondingly annular passages positioned lengthwise, but the chambers of each series are preferably not in communication with one another.

The communicating orices of the chambers of each section progressively increase in number in the direction of the gas ilow. Although, as 15 illustrated herein, each section has substantially the same progressive increase in effective exhaust area, it will be obvious that the communieating orifices along the channel, as well as the chambers of each series, may be progressively increased either from the same number of openings as that shown at the inner portion of the channel or from progressively increasing number of openings so that there will be a progressive increase in the effective exhaust area of the silencer substantially throughout the length thereof and also for each section.

The number of communicating orifices and the rate of increase in the effective opening of each section will depend to a great extent upon the relative rate of ow, rate of expansion of the gaseous medium and the limiting back pressure.

The silencer also provides for the gaseous medium to be divided in each section into. two branches that are caused. to abut one another immediately prior to passing through the communicating o'riiices between the chambers thereof and to ow through each section in a sinuous path by arranging the communicating orifices only along one side of each chamber wall or jacket 40 and by having the orifices of adjacent jackets substantially diametrically disposed.

The silencer may be further modified by providing a back pressure chamber wherein a pressure of the gaseous medium is built up such that it will tend to effect a smooth ow of the gaseous medium to atmosphere rather than a pulsating ow. This variation is not always necessary but is applied where maximum efficiency of silencing is desirable. The results of tests made at the Material Division of the U. S. Army Air Corps with a silencer embodying this invention have shown that substantially 97 per cent of the total sound energy of an airplane with a 2:1 geared engine was dissipated by the silencer. Tests of the engine as a separate unit would show a greater reduction.

Referring to Fig. 1 of the drawings, which shows a preferred form of this invention, the numeral IIJ designates a circular tube or channel of sub stantially the same cross-section as the exhaust tube I2 of the engine. Two cylinders I4 and I3 are mounted on the tube I8 in concentric relation therewith and in spaced relation with the tube and with one another. The distance between the walls of the several cylinders is small so as to provide narrow passages as Well as to produce a silencer the overall cross-sectional area of which is slightly greater than the cross-sectional area of the exhaust tube. A series of spacer rings E8 are mounte-d on tube IU between the outer wall of tube Il] and the inner wall of cylinder I 4. The number of these spacer rings will depend upon the number of side branches that may be desired. There are also provided a series of spacer rings 20 between the outer Wall of cylinder I6 and the inner Wall of cylinder I4. These spacer rings serve to prevent the walls of the cylinder from buckling inward as well as in thefcapacity of bulkheads which determine the several side branches 22. By having each spacer connected to only one of its adjacent walls and the corresponding ends 24 and 26 of the cylinders I4 and I6 respectively welded to each other and to the tube I0 by a weld 28 with the respective opposite ends 30 and 32 of these tubes free to slide relative to one another and to the tube I0, the tubes will not be stressed under expansion and contraction with changes in temperature.

The tube or channel I0 extends beyond the sections 22 and a baiile plate or cut-out 34 is pivotally supported therein by bearings 35 that are welded on opposite sides of the tube I0. The, baffle plate is positioned at a predetermined point beyond the sections 22 so that the extensionv 36 and the baffle plate provide a chamber of predetermined capacity. The location and volume of the chamber 38 are experimentally determined from the total Volume and length of the silencer and exhaust tube and bear a definite relation thereto.

The operation of the silencer is as follows:

The exhaust gases coming from the engine enter through I2 to tube I0. These gases flow in pulsations which result from the explosions in the engine cylinders.

These pulsating gases flow along tube I D and partially escape through holes or ports 40 into the space between tubes I0 and I4. This partial escape of gas through holes or ports 4l) tends to reduce the peak pressure of that individual gas pulsation.

The gases passing through holes or ports 4l] into the space between I0 and I4 divide into approximately equal parts and ilow in both directions around tube I4 and meet at 42, which are on the opposite side of the silencer from ports 43. The speed of these separate gas streams is converted at impact into a local pressure, which inn creases the volume of their ow through ports 42 into the space between tubes I4 and I6 resulting in a further decrease in pressure between tubes I4 and I6 than would normally result.

The gases flowing through ports 42 into the space between tubes I4 and I6 again divide into approximately equal parts and flow in both directions around tube I4, meeting at ports 44. These ports are similar to ports 40 and 42, but greater 44 over ports 42 and of ports 42 over ports 4U is employed to take care of the increased volume of the exhaust gases due to expansion. The total cross-sectional area of all the ports in either I0, I4 or I6 is such as to provide for a gas flow of sufficient volume to prevent back pressure building up due to expansion of gases and which would result in excessive loss of engine power. Ports 40, 42 and 44, and the tortuous path of the exhaust gases through the silencer with the abutting of the gas streams as described and the interferences due to passing through ports 4i), 42 and 44, the changing of direction in passing through the curved passages between the jackets and the narrow chambers of each section, have the particular function of destroying the higher sound frequencies generated by the rapid cornbustion of fuel in the engine cylinders.

The lower sound frequency produced by the volume and pressure of the engine pulsations of the exhaust gases are dampened out by use of chamber 38.

Gases from one exhaust pulsation, which have not passed out to the atmosphere through ports 40, 42 and 44, as described above, continue their flight into chamber 33, strike baiile plate 34 and rebound backinto the body of the silencer, escaping through ports 4U, 42 and 44 in the manner described above before the next exhaust pulsation can interfere with this action. Although there is a loss of pressure in a particular pulsation due to escape of a part of its volume through ports 40, 42 and 44, the expansion of the gases maintains a speed sufli'cient to complete the above cycle. To control the completion of the cycle of flow of one pulsation, as described above, baie plate 34 of chamber 38 is so located with respect to the body of the silencer that each pulsation may complete this cycle of flow without interferencey from the preceding or the following one.

When the bafile plate 34 of chamber 38 is in closed position, the chamber 38 may be regarded as operating similar to an electrical condenser in parallel with the channel or tube I0 and ther side branches 22. When, however, the baie plate is open, the main flow of the gas is through the baffle plate opening and the side branches may be regarded as operating similar to electrical f1ltersthat eliminate certain undesired frequencies'` Chamber 38 may be omitted and the silencer closed oi flush with the ends of the outer tubes I4 and I6 where more complete silencing is unimportant. If the chamber 33 is not used tubes I0, I4 and I 6 should be lengthened so as to allow practically all of the exhaust gas to escape in increments along the length of the silencers leaving but very little high pressure gas to strike the end of the silencer.

Fig. 4 shows another embodiment of this invention. The construction shown in this view is the same as in Fig, 1, except that there is provided a U-shaped deiiector 46 that is open at one end only and surrounds the bottom portion of the tube I6 containing the exhaust openings or ports 44 for the entire length of the silencer. The open end of this deiiector is provided with an extension tube 43 to direct the gases as desired.

Fig.'6 shows afurther embodiment of this in- Vention. The construction of the silencer in this view is the same as in Fig. 1 except that the cylinders 50 and 52 surrounding tube II) are eccentrically disposed withV respect to the latter tube, and to each other. 'Ihe arrangement of the ports is identical with the correspondingly positioned ports of the silencer shown in Fig. 2..

A still further variation of this invention isy 'shown in Fig. "l, which `the silencer is made from one continuous sheet of metal. The sheet is wound in such a manner and the ports 54 and 56 so arranged that the gases passing through ports 54 are directed circumferentially around through the sectional chambers 58 of the silencer to ports 56 whence they escape to atmosphere.

Various changes may be made in the design and construction shown and illustrated herein without departing from the spirit of this invention.

We claim:

1. A device for conducting a ow of gas and limiting the transmission of wave pulsations therethrough, comprising, a conducting channel closed at one end and open at the other to receive said gas having a plurality of longitudinally disposed ports, a perforated tube of greater diameter than said channel surrounding the same to enclose said ports and spaced therefrom, said tube being rigidly connected with the channel at one end but free at the other to prevent stressing of the walls of said channel and tube under expansion and contraction thereof and radial partitions between the Walls of said tubes to provide a plurality of separate axially arranged chambers, each chamber having direct communication with atmosphere.

2. A device for conducting a flow of gas and limiting the transmission of wave pulsations therethrough, comprising, a conducting channel that is closed at one end and having a plurality of longitudinally disposed ports, a plurality of tubes of increasing diameter greater than said channel surrounding said channel and spaced therefrom and from one another, said tubes being perforated along their lengths and being rigidly connected wth the channel at one of their ends but free at the other to prevent stressing of the Walls of said channel and tube under expansion and contraction thereof and radial partitions between adjacent walls of said tubes to provide a plurality of separate axially arranged side branches, each branch having direct communication with atmosphere.

3. A device for conducting a flow of gas and limiting the transmission of wave pulsations therethrough, comprising, a conducting channel that is closed at one end and having a plurality of longitudinally disposed ports, a plurality of perforated tubes of increasing diameter greater than said channel surrounding said channel and spaced therefrom and from one another radial partitions between adjacent walls of said tubes to provide a series of separate gas conducting branches laterally disposed with respect to and surrounding said tubes, said channel being rigidly connected with the channel at one of their ends but free at the other to prevent stressing of the walls of said channel and tube under expansion and contraction thereof.

4. A device for conducting a iiow of gas and limiting the transmission of wave pulsations therethrough, comprising a conducting tube having closure means at one end and being open at the other to receive said gas, and a plurality of gas conducting branches laterally disposed and adjacent said tube, each of said branches being provided with inlet and outlet openings to establish separate communication between said tube and atmosphere, the said branches extending from the open end of said tube toward the closed end thereof for a given length of said conducting tube to provide a gas containing reservoir extending substantially beyond said branches and having a capacity such that the pressure variation in the ow of gas through said branches is reduced to a maximum consistent with minimum back pressure.

5. A device for conducting a flow of gas and limiting the transmission of pulsations therethrough, comprising a conducting tube having means for closing one end to provide a non-dissipative portion and being open at the other and along a length thereof to provide a dissipative portion, said non-dissipative portion being adjusted to such a length that, when closed, will cause a material reduction in the sound energy of said pulsations, and a plurality of gas conducting branches laterally disposed and adjacent said tube, each of said branches including a plurality of chambers in communication with each other, the effective open areas of said inlet and outlet openings of said chambers progressively increasing in the direction of travel of said gases from conducting tube to atmosphere.

6. A device for conducting a ow of gas and limiting the transmission of pulsations therethrough, comprising a conducting tube having means for closing one end to provide a non-dissipative portion and being open at the other and along a length thereof to provide a dissipative portion, said non-dissipative portion being adjusted to such a length that, when closed will cause a material reduction in the sound energy of said pulsations, and a plurality of gas conducting branches laterally disposed and adjacent said tube, each of said branches being provided with inlet and outlet openings consisting respectively of a plurality of relatively small ports arranged longitudinally of said branches to establish communication between said tube and atmosphere, the dimensions of said branches and their respective openings being such that the acoustic length of said tube is negligibly affected thereby.

7. A device for conducting a flow of gas and limiting the transmission of pulsations therethrough, comprising a conducting tube having means for closing one end to provide a non-dissipative portion and being open at the other and along a length thereof to provide a dissipative portion, said non-dissipative portion being adjusted to such a length that, when closed, will cause a material reduction in the sound energy of said pulsations, and a plurality of gas conducting branches laterally disposed and adjacent said tube, each of said branches establishing substantially separate communication between said channel and atmosphere and including at least one or more chambers, said chamber or chambers having relatively small ports longitudinally arranged in the walls thereof, the ports of one wall being oppositely disposed with respect to the ports of another so that the gas iiow is divided upon entering through the ports of one wall and caused to abut before passing through the ports of another.

8. A device for conducting a flow of gas and limiting the transmission of pulsations therethrough, comprising a conducting tube having means for closing one end to provide a non-dissipative portion and being open at the other and along a length thereof to provide a dissipative portion, said non-dissipative portion being adjusted to such a length that, when closed, will cause a material reduction in the sound energy of said pulsations, and a plurality of gas conducting branches laterally disposed and adjacent said tube, said branches being respectively provided with inlet and outlet openings to establish substantially separate communications between said tube and atmosphere and having such dimensions that the acoustic length of said tube is negligibly affected thereby, said non-dissipative portion having a capacity such that the pressure built-up therein by the gas flow will smoothen out the pressure variations of said pulsations and thereby obtain a substantially uniform flow of gas through said branches,

9. A device for conducting a flow of g-as and limiting the transmission of pulsations therethrough, comprising a conducting tube having means for closing one end to provide a non dissipative portion and being open at the other and along a length thereof to provide a dissipative portion, said non-dissipative portion being adjusted to such av length that, when closed, will cause a material reduction in the sound energy of said pulsations consistent with obtaining a minimum of back pressure, and a plurality of gas conducting branches laterally disposed and adjacent said tube, said branches being respectively provided With inlet and outlet openings to establish substantially separate communications between said tube and atmosphere and having such dimensions that the acoustic length of said tube is negligibly afected thereby.

10. A device for conducting a ovv of gas and limiting the transmission of pulsations therethrough, comprising a conducting tube having means for closing one end to provide a non-dissipative portion and being open at the other and along a length thereof to provide a dissipative portion, said non-dissipative portion being adjusted to such a length that, when closed, will cause a material reduction in the sound energy of said pulsations consistent with obtaining a minimum of back pressure, and a plurality of gas conducting branches laterally disposed and adjacent said tube, each of said branches being provided with inlet and outlet openings to establish separate communication between said tube and atmosphere, the dimensions of said branches and their respective openings being such as to dissipate the energy of the high frequency sound Waves of the direct and reflected Wave pulsations and such that the acoustic effect of said tube is negligibly affected thereby.

11. A device for conducting -a flow of gas and limiting the transmission of pulsations therethrough, comprising a conducting tube having means for closing one end to provide a non-dissipative portion and being open at the other and along a length thereof to provide a dissipative portion, said non-dissipative portion being adjusted to such a length that, when closed, will cause a material reduction in the sound energy of said pulsations, and a plurality of gas conducting branches of diierent acoustic lengths laterally disposed and adjacent said tube, said branches being respectively provided with inlet and outlet openings to establish substantially separate communications between said tube and atmosphere and having such dimensions that the acoustic length of said tube is negligibly aiected thereby.

l2. A device for conducting a now of gas and limiting the transmission of pulsations therethrough, comprising a conducting tube having means for closing one end to provide a non-dissipative portion and being open at the other and along a length thereof to provide a dissipative portion, said non-dissipative portion being adjusted to such a length that, when closed, will cause a material reduction in the sound energy of said pulsations consistent with obtaining a minimum of back pressure, and one or more branches laterally disposed and adjacent said tube for conducting said gases to atmosphere, said branch or branches having communication With said tube in the region of a nodal point or points along s-aid tube and having the communieating openings thereof of such dimensions as to negligibly affect the acoustic length of said conducting tube.

HOWARD H. COUCH. DUDLEY W. WATKINS. JAMES B. BRELSFORD. 

